Missing URL in multipart message

We use RT here at the office for ticketing/support. I noticed something today after the upgrade to 5.0.6 that didn't seem quite right. Every ticket that comes in from a user has a URL to the ticket in the system for easy clicking, but that URL has suddenly disappeared.

The system sends the requests as multipart/mixed and Zimbra seems to be trying to interpret part of the text/plain as text/html. For whatever reason, the URL was configured to display like this:

Code:

Ticket <URL: http://etc.etc.com/rt/etc?id=1111 >

So the only thing I can assume is that it's seeing those < and >, and treating it like an HTML tag, albeit an invalid one, which makes it not display at all. When I remove those 2 characters, the URL appears just fine, and is picked up by the zimlet. I've re-configured our RT to get around this, but it may affect other things at some point as well.

This is an example of the email that it sends (headers partially stripped):